The present invention relates to an improved sub-surface, or in-ground/in-water, heat exchange means incorporating a sub-surface heating mode refrigerant flow regulating device and a cooling mode refrigerant flow regulating device by-pass means, so as to enable additional refrigerant flow around the regulating device in the cooling mode, for use in association with any direct expansion heating/cooling system, or partial geothermal heating/cooling system, utilizing sub-surface heat exchange elements as a primary or supplemental source of heat transfer.
Ground source/water source heat exchange systems typically utilize fluid-filled closed loops of tubing buried in the ground, or submerged in a body of water, so as to either absorb heat from, or to reject heat into, the naturally occurring geothermal mass and/or water surrounding the buried or submerged tubing. Water-source heating/cooling systems typically circulate, via a water pump, water, or water with anti-freeze, in plastic underground geothermal tubing so as to transfer heat to or from the ground, with a second heat exchange step utilizing a refrigerant to transfer heat to or from the water, and with a third heat exchange step utilizing an electric fan to transfer heat to or from the refrigerant to heat or cool interior air space.
Direct expansion ground source heat exchange systems, where the refrigerant transport lines are placed directly in the sub-surface ground and/or water, typically circulate a refrigerant fluid, such as R-22, in sub-surface refrigerant lines, typically comprised of copper tubing, to transfer heat to or from the sub-surface elements, and only require a second heat exchange step to transfer heat to or from the interior air space by means of an electric fan. Consequently, direct expansion systems are generally more efficient than water-source systems because of less heat exchange steps and because no water pump energy expenditure is required. Further, since copper is a better heat conductor than most plastics, and since the refrigerant fluid circulating within the copper tubing of a direct expansion system generally has a greater temperature differential with the surrounding ground than the water circulating within the plastic tubing of a water-source system, generally, less excavation and drilling is required, and installation costs are lower, with a direct expansion system than with a water-source system.
While most in-ground/in-water heat exchange designs are feasible, various improvements have been developed intended to enhance overall system operational efficiencies. Several such design improvements, particularly in direct expansion/direct exchange geothermal heat pump systems, are taught in U.S. Pat. No. 5,623,986 to Wiggs; in U.S. Pat. No. 5,816,314 to Wiggs, et al.; in U.S. Pat. No. 5,946,928 to Wiggs; and in U.S. Pat. No. 6,615,601 B1 to Wiggs, the disclosures of which are incorporated herein by reference. Such disclosures encompass both horizontally and vertically oriented sub-surface heat geothermal heat exchange means.
Other predecessor vertically oriented geothermal heat exchange designs are disclosed by U.S. Pat. No. 5,461,876 to Dressler, and by U.S. Pat. No. 4,741,388 to Kuriowa. Dressler's '876 patent teaches the utilization of several designs of an in-ground fluid supply and return line, with both the fluid and supply lines shown as being the same size, and not distinguished in the claims, but neglects to insulate either the fluid return line or the fluid supply line, thereby subjecting the heat gained or lost by the circulating fluid to a “short-circuiting” effect as the supply and return lines come into close proximity with one another at various heat transfer points. Dressier also discloses the alternative use of a pair of concentric tubes, with one tube being within the core of the other, with the inner tube surrounded by insulation or a vacuum. While this multiple concentric tube design reduces the “short-circuiting” effect, it is practically difficult to build and maintain and could be functionally cost-prohibitive, and it does not have a dedicated liquid line and a dedicated vapor line. Kuriowa's preceding '388 patent is similar to Dressler's subsequent spiral around a central line claim, but better, because Kuriowa insulates a portion of the return line, via surrounding it with insulation, thereby reducing the “short-circuiting” effect. However, Kuriowa does not have a dedicated liquid line and a dedicated vapor line. The lowermost fluid reservoir claimed by Kuriowa in all of his designs can work in a water-source geothermal system, but can be functionally impractical in a deep well direct expansion system, potentially resulting in system operational refrigerant charge imbalances, compressor oil collection/retention problems, accumulations of refrigerant vapor pockets due to the extra-large interior volume, and the like. Kuriowa also shows a concentric tube design preceding Dressler's, but it is subject to the same problems as Dressler's. Further, both Dressler's and Kuriowa's designs are impractical in a reverse-cycle, deep well, direct expansion system operation since neither of their primary designs provide for, or claim, an insulated smaller interior volume sized liquid line and an un-insulated larger interior volume sized vapor line, which are necessary to facilitate the system's most efficient operational refrigerant charge and the system's compressor's efficient refrigerant supply and return capacities.
Generally, a design which insulates the supply line from the return line and still permits both lines to retain natural geothermal heat exchange exposure, such as a thermally exposed, centrally insulated, geothermal heat exchange unit, as taught by Wiggs in U.S. patent application Ser. No. 10/127,517, which is incorporated herein by reference, would be preferable over non-insulated lines and over designs which insulate a portion of one sub-surface line. However, while Wiggs' '517 Application is an improvement over prior art, in a sub-surface soil application, it could still be subject to some minor short-circuiting effects and to some potentially adverse vapor formation in the liquid line at undesirable locations or times.
In direct expansion applications, supply and return refrigerant lines may be defined based upon whether they supply warmed refrigerant to the system's compressor and return hot refrigerant to the ground to be cooled, or based upon the designated direction of the hot vapor refrigerant leaving the system's compressor unit, which is the more common designation in the trade. For purposes of this present invention, the more common definition will be utilized. Hence, supply and return refrigerant lines are herein defined based upon whether, in the heating mode, warmed refrigerant vapor is being returned to the system's compressor, after acquiring heat from the sub-surface elements, in which event the larger interior diameter, sub-surface, vapor/fluid line is the return line and evaporator, and the smaller interior diameter, sub-surface, liquid/fluid line, operatively connected from the interior air handler to the sub-surface vapor line, is the supply line; or whether, in the cooling mode, hot refrigerant vapor is being supplied to the larger interior diameter, sub-surface, vapor fluid line from the system's compressor, in which event the larger interior diameter, sub-surface, vapor/fluid line is the supply line and condenser, and the smaller interior diameter, sub-surface, liquid/fluid line is the return line, via returning cooled liquid refrigerant to the interior air handler, as is well understood by those skilled in the trade. In the heating mode the ground is the evaporator, and in the cooling mode, the ground is the condenser.
None of the above-said prior art addresses an improved means of designing a direct expansion system for a reverse-cycle heating/cooling system operation via insulating only one smaller interior diameter, sub-surface, line, designed primarily for liquid/fluid refrigerant transport, which smaller line may be utilized as a supply line in the heating mode and as a return line in the cooling mode, and of not insulating at least one, or two or more combined, larger interior diameter, sub-surface, lines, designed primarily for vapor/fluid transport, which can provide expanded surface area thermal heat transfer as return lines in the heating mode and as supply lines in the cooling mode. While at least two, larger combined interior diameter, vapor/fluid refrigerant transport lines, operatively connected to one, smaller interior diameter, liquid/fluid refrigerant transport line would generally be preferable because of the resulting expanded, and spaced apart, heat transfer surface contact area, instances may arise where only one, larger interior diameter, vapor/fluid refrigerant line, operatively connected to one, smaller interior diameter, liquid/fluid refrigerant line could also be preferable, or where a larger interior diameter vapor/fluid refrigerant line is spiraled around a centrally located, insulated, smaller diameter liquid/fluid refrigerant line could be preferable.
Where a close to zero-tolerance short-circuiting effect is desirable, and where the time and expense of constructing other designs, such as a concentric tube within a tube, or a spiraled single fluid return line and single fluid supply line of the same sized interior diameters, could be financially, or functionally and/or efficiently, prohibitive in a deep well direct expansion application, and where the thermal exposure area of a single geothermal heat transfer line, or tube, could be too centralized and too heat transfer restrictive, a system design improvement would be preferable which incorporated a cost-effective installation method, capable of operating in a reverse-cycle mode in a sub-surface direct expansion application, with close to zero-tolerance short-circuiting effect, with expanded sub-surface heat transfer surface area capacities, and with a liquid refrigerant trap means at the bottom of the sub-surface heat exchange lines to assist in preventing refrigerant vapor migration, from the refrigerant vapor line into the refrigerant liquid line, as is taught in Wiggs' pending U.S. patent application Ser. No. 10/251,190, which is incorporated herein by reference. However, none of the above-said prior art addresses the most efficient means of regulating the refrigerant fluid flow through the sub-surface refrigerant transport lines when a direct expansion system is operating in the heating mode, and of permitting optimum refrigerant flow rate around the regulating device when the reverse-cycle system is operating in the cooling mode.
Virtually all high-efficiency heat pump systems, including direct expansion heat pumps, utilize thermal expansion valves to regulate refrigerant flow through the evaporator, which is the exterior heat exchanger in the heating mode, and which is the interior air handler in the cooling mode. In the heating mode, for example, the thermal expansion valve is typically a self-adjusting thermal expansion valve, which valve will generally and ideally be situated in the refrigerant transport line at a point as close as possible to where the refrigerant fluid enters the evaporator, and which valve is operatively connected to a floating bulb. The floating bulb senses superheat levels and sends signals to the valve to adjust the refrigerant flow rate so as to obtain efficient system operation, depending on changing heating load and superheat conditions. The operation of self-adjusting thermal expansion valves is well understood by those skilled in the art.
While use of self-adjusting thermal expansion valves is appropriate in the heating mode for air-source and water-source heat pump systems, where the copper heat exchange tubing is all in relatively close proximity and where the valves are readily accessible for servicing, the common use of such self-adjusting thermal expansion valves in direct expansion heat pump systems can be relatively inefficient because the design refrigerant flow tubing length in the evaporator is often 100 feet, or more. Hence, in a typical direct expansion system, operating in the heating mode, any self-adjustment by the thermal expansion valve takes an inordinate amount of time to take effect and to be sensed by the valve. The valve, during the interim, continues to modulate and fluctuate refrigerant flow rates as it “hunts” for an optimum setting. This “hunting” results in periodic inefficient system operation and in periodic undesirable decreases in supply air temperatures.
The typical utilization of self-adjusting thermal expansion valves in the heating mode of direct expansion heat pump systems presents problems other than the “hunting” concerns. Namely, since such valves are bulky, and may periodically be in need of servicing or replacement, they must be installed in an accessible location, which has historically either been inside the compressor unit box, far from the actual evaporator, or near the ground surface, as close as possible to the point where the refrigerant enters the sub-surface evaporator, but still some distance away from the actual sub-surface evaporator. This is a problem because to operate at maximum efficiencies, the expansion device should generally be as close as possible to the actual evaporator.
Thus, the historical perception by some, that a self-adjusting thermal expansion valve should be utilized in the heating mode of a direct expansion system because it provides the highest operational efficiencies, is subject to serious question because of the necessary distance it must be located from the evaporator and because of inherent “hunting” problems. In fact, the longer and/or the deeper the sub-surface evaporator heat exchange lines are in a sub-surface direct expansion system, the greater the “hunting” problem becomes with a self-adjusting thermal expansion valve.
However, the use of a self-adjusting thermal expansion valve is generally always appropriate in the cooling mode of a high-efficiency heat pump system, regardless of the type of heat pump utilized, including direct expansion heat pumps, since the valve and the floating bulb, which are readily accessible for servicing, can generally always efficiently function together because of the relatively close proximity of the heat exchange tubing within the interior air handler.
One alternative method of regulating refrigerant flow in the heating mode of a direct expansion heat pump is to install a manually adjusting thermal expansion valve in lieu of a self-adjusting thermal expansion valve. Such a valve will eliminate hunting problems since it will not automatically adjust its own setting. However, such a manually adjusting valve generally must still be placed in an accessible location, which could be hundreds of feet above the actual evaporator in a DWDX application. Further, experience has shown that such a manually adjusting valve, when utilized in a near-surface direct expansion application (within 100 feet of the surface), typically requires at least two manual adjustments per year in order for the system to provide adequate and efficient heat. One such adjustment is required in the fall, at the beginning of the heating season, when the ground surrounding the sub-surface heat exchange tubing is relatively warm, as a result of summer conditions and the system's preceding cooling mode operation, which has been rejecting heat into the ground area surrounding the sub-surface heat exchange tubing. Generally, at least one other adjustment is required during the winter, as the ground surrounding the sub-surface heat exchange tubing has cooled down to winter-time operational temperatures as a result of heat being extracted by the system in its heating mode of operation. A reasonable manual expansion valve setting for a direct expansion system, when the sub-surface ground is warm, is not the same reasonable setting for when the ground is cool. The construction, the operation, and the reasonable settings of a manual adjusting thermal expansion valve is well understood by those skilled in the art.
Thus, the use of a manually adjusting thermal expansion valve in a direct expansion system, particularly in a DWDX system, while eliminating the hunting problem of a self-adjusting thermal expansion valve, has its problems. A manually adjusting valve is comparatively bulky, must be installed in an above ground and/or accessible location, and, as explained, typically must be adjusted and serviced at least twice per year.
Another alternative method of regulating refrigerant flow in the heating mode is to install a refrigerant fluid distributor with a fixed restrictive hole, or orifice, inside, and typically at the center of, a floating, bullet-shaped, finned, piston, which device is commonly referred to by several designations, such as a piston metering device, a single piston metering device, a floating piston assembly, and a pin restrictor. In the heating mode, the piston, within a casing/housing, moves toward a restrictive seal, which only permits refrigerant fluid flow through the piston hole, or orifice, in the center, thereby regulating the amount of refrigerant entering the evaporator. In the cooling mode, as the refrigerant flow changes direction, the piston moves back, or floats back, toward a less restrictive seal which permits refrigerant fluid flow through the hole, or orifice, as well as additionally through the gaps between the exterior fins on the piston. The specific construction and operation of piston metering devices, including the casings/housings within which they are enclosed, are well understood by those skilled in the art. Since a piston metering device has a fixed orifice, the refrigerant fluid flow rate cannot be adjusted, other than by pressure, so as to accommodate changing exterior load requirements, and has, therefore, generally been considered less efficient and has generally not been used in high-efficiency systems such as direct expansion heat pumps. Instead, many direct expansion heat pump systems utilize self-adjusting thermal expansion valves because of their well-known advantages and improved performance in other heat pump designs, which advantages have previously been commonly, although incorrectly, believed by some to equally apply in a direct expansion application.
In fact, a piston metering device can be more efficient in the heating mode of a direct expansion application than expansion valves, particularly in a DWDX application, because the ground at a depth of more than 100 feet is seasonally less affected by changing, and widely varying, above-ground, near surface, atmospheric temperatures, and hunting, or seasonal valve setting adjustments, for an optimum setting may not be necessary. A piston metering device will eliminate hunting concerns, and, since it is not bulky, can be installed in either an above-ground accessible location, or directly at the commencement of the evaporator segment of a sub-surface direct expansion system where efficiencies are generally best.
However, a reason exists for not using a conventional piston metering device alone in a reverse cycle direct expansion (also commonly referred to as direct exchange) heating/cooling system. Testing has also shown that a properly sized single piston metering devise in a Deep Well Direct eXpansion (“DWDX”) system (deep well is herein defined as where sub-surface heat exchange lines are in excess of 100 feet deep), can impair the optimum refrigerant fluid flow when the system is operating in its reverse cycle cooling mode, as the available refrigerant fluid passageway through the hole in the center of the bullet, together with the available fluid passageway around the outside of the bullet through the fins, can be inadequate to maintain an optimum cooling design refrigerant fluid flow rate. This is because the added pressure, via gravity upon the liquid refrigerant in a DWDX application, can dictate the use of a slightly undersized conventional piston metering device, which device would normally be sized to match the compressor in a conventional heat pump application, but which slightly undersized device in a DWDX application, because of the additional liquid pressure, still achieves the compressor design flow rate in the heating mode, but which undersized device can be a potential impairment to the compressor design flow rate in the cooling mode.
Testing has also alternately shown that, in lieu of utilizing an slightly undersized conventional metering device in a DWDX system application so as to offset the additional liquid pressure, that a more conventionally sized (not undersized) metering device, when sized to match the system's compressor and not the system's design load capacity, can be utilized in a DWDX system application so long as the conventional refrigerant charge is one of slightly adjusted and slightly reduced, which, in an alternate manner, will provide the same desired ultimate effect of offsetting the additional liquid pressure present in the heating mode of a DWDX system. While conventional heating designs call for the metering device to match the system's design load capacity, testing has shown that, for optimum system performance, the metering device, for any direct expansion heat pump system operating in the heating mode, and particularly in a DWDX system, should be sized to match the system's compressor design capacity (meaning the compressor's design capacity in tons, where one ton equals 12,000 BTUs), and not the system's heating design capacity, which may differ.
Typically, should one elect to provide a conventionally sized metering device, sized to match the system's compressor and not the system's design load capacity as explained, rather than a slightly undersized metering device, some additional space will be automatically provided for the refrigerant to flow through and around the metering device in the cooling mode, as the orifice in the metering device will be larger.
If one elects to install a piston metering device in an above ground and/or an accessible location, the piston size can be easily changed to accommodate changing temperature conditions, or multiple such devices of varying sizes can be installed in series with a pressure and/or temperature means to automatically activate the preferred sized device and to deactivate the rest, by means of a remotely actuated valve such as a solenoid valves, or the like. The installation and operation of remotely actuated valves, such as solenoid valves, and the like, are well understood by those skilled in the art, and, therefore, are not shown herein.
Consequently, a means to provide an efficient refrigerant flow regulating device in a direct expansion, reverse-cycle, heating/cooling system, operating in the heating mode, without “hunting” problems, which device does not necessarily require maintenance access although it would preferably be accessible, which device is either in close proximity to the actual evaporator or which device can optionally compensate for significant changes in sub-surface temperature environments without the need for manual adjustments, and which device does not inhibit the full refrigerant flow in a reverse cycle cooling mode operation, would be preferable. The present invention provides a solution to these preferable objectives, as hereinafter more fully described.